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Master Gardeners: The Mighty Oak

A typical oak tree will live to have tens of thousands of its acorns devoured by insects, birds, and mammals. However, that is but the beginning of an acorn´s struggle for survival.

Acorns not eaten may drop where it is too shady, hot, or dry to produce a young tree. A lucky few land in a good spot, perhaps buried by a bird or mammal that forgets its cache. Fall rains begin germination and growth, but even under the best conditions few seedlings survive, only to encounter drought, animal browsing, insects, wildfire and disease. Yet, those that do survive can become trees that live for centuries.

Five oak species are found in the Mother Lode, each with its own preferred growing environment. The swirling textures and colors of oak landscapes reflect the hidden, underlying patterns of soil and moisture. These influence the type of oak that survive and thrive, perhaps combined with conifers, thus forming oak communities.

Deciduous Oaks shed their leaves in the fall. However, to conserve moisture in particularly dry years, they may drop their leaves even before summer´s end. Blue Oaks with their blue-green leaves are usually found below 2000 ft. They are especially drought tolerant, often growing on ridges to avoid moist drainage areas. On the other hand, the Valley Oak, with deeply lobed leaves, grows mostly near streams where the soil is moist and deep. Look for Black Oaks above 3000 ft. in mixed confer forests. Their large, lobed leaves turn gold in the fall providing much of our beautiful fall color.

“Live Oaks” are evergreen. Canyon Live Oak may be found in canyons, growing up the sides on steep, hot, rocky slopes. The Interior Live Oak is most common in the 2000 to 3000 ft. elevation, often with many trunks resulting from fire. You will see it growing in mixed forests with Gray Pine and Blue Oak.

Fire. Our drought and high summer temperatures are ideal for the spread of both natural and human-set fires. Oaks over the millennia have evolved to tolerate, even to benefit, from fast burning fire. Thick bark may protect mature trees; seedlings and saplings send up new shoots. Fire reduces root and light competition from other plants. Insects and fungi are temporarily eliminated and soil minerals may become more available. However, intense fire resulting from buildup of long accumulated brush can kill even mature trees.

Relentless change. Although there are seasons with good acorn growth, many areas of the state are seeing little replacement of oak populations. There are many reasons.

European immigrants brought weeds, livestock and fire suppression—causing inevitable impact on native flora and fauna. Seeds of aggressive weeds and annual grasses arrived as stowaways in hay and grain, their growth now free of the diseases and insects that kept them in check in the Old World. Predator control created abundant and hungry deer herds and colonies of rodents. Agriculture, livestock grazing and soil compaction, disease, urbanization, and industry increase destruction and decrease available land.

Conservation strategies. Many of our stately oaks are 300 years old and more, yet they can succumb to stresses of the modern landscape. Oaks need summer drought; turn off the sprinkler under your trees, especially near the trunk. Keep construction and paving away from the drip line to prevent compaction and altering the soil level.

The national and state park systems, many other public agencies, and environmental groups are working to preserve and replace oaks. For example, Caltrans has placed over 10,000 plants along the new Sonora Bypass, many of them natives including Blue, Black, Valley, and Interior Live Oaks. Although there is a temporary watering system, ultimate survival depends on Mother Nature.

Within each acorn lies the budding potential for centuries of splendor, but at best, it will be mid-century before new oaks reach maturity. Let´s strive to see that happen.

For more information about caring for your oaks and establishing new ones, call the Tuolumne County Master Gardener office at 533-5696.

See you in the garden.

Vera Strader is a Sonora-based Master Gardener who treasures both native oaks and the wildlife that depends on them. Her garden is certified as a National Wildlife Federation Backyard Wildlife Habitat.